This invention relates to sensors and sensor components that have multilayer membranes and methods of making and using the sensors and sensor components. In addition, the invention relates to enzyme electrodes and optodes with multi-layer analyte-flux limiting membranes and methods of making and using the optodes and the electrodes.
Miniature biosensors utilizing enzyme-containing optodes and electrodes for monitoring biochemicals often include mass-transport controlling membranes. The membranes can affect some or all of the characteristics of the optodes or electrodes, including their sensitivity, size, apparent stability, dynamic range and selectivity. Micro-membranes for use with miniature biosensors typically cannot be easily cut to size from preformed membranes and if cut by a precision tool, such as a laser or an electron beam, their placement on and attachment to the surface of an electrode or optode can be difficult.
The reproducible casting of micro-membranes can also be difficult. For cast micro-membranes, the pore sizes and their distribution are typically determined by the relative rates of nucleation and mass-transport during generation of the membrane by phase separation as a result of solvent evaporation. The outcome of the simultaneously occurring nucleation and the mass transport processes depends on the evolution (meaning the time-dependence during the solvent evaporation) of the viscosity, the concentrations of the solvent and the non-solvent, and the membrane""s leached phase and its residual phase. These are affected by time-dependent temperature gradients and by the time-dependent gradient of the partial pressure of the evaporating solvent over a droplet, the dimensions of which shrink and are a function of the time-dependent contact angle with the wetted surface.
Generally, the present invention relates to electrodes and optodes having membranes to reduce analyte flux or reduce interferent flux or both. One embodiment is a sensor that includes a sensing layer disposed on a substrate and a multilayer flux-limiting membrane disposed over the sensing layer. The membrane includes a first layer disposed on and bound to the sensing layer and one or more additional layers disposed on and bound to the preceding layers of the membrane. The substrate can have a conductive material upon which the sensing layer is disposed to form an electrode or an optical material, such as an optical fiber, upon which the sensing layer is disposed to form an optode. As an example, the membrane includes at least two layers; one of which is a polycationic layer or a polyanionic layer. Optionally, the membrane includes at least one layer that has functional groups that can capture transition metal ions.
Another embodiment is a method of making a sensor. A sensing layer is disposed on a substrate. A first membrane layer is disposed on and binds to the sensing layer. One or more subsequent membrane layers are disposed over the first membrane layer, each of the subsequent membrane layers binding to the immediately preceding membrane layer. For example, the membrane layers can be formed by chemisorption or reactive adsorption.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and the detailed description which follow more particularly exemplify some but not all of these embodiments.